1. Field of the Invention
The present invention relates to a vehicle-use battery monitor apparatus for detecting a charging/discharging current of a battery mounted on a vehicle such as a passenger car and a truck.
2. Description of Related Art
There is known a configuration in which a ratio of an energization time to a total time including the energization time and a de-energization time of an exciting coil of a vehicle alternator is calculated to detect the power generation work of the vehicle alternator, and an intake air quantity at idling of a vehicle engine is corrected on the basis of the detected power generation work. For example, refer to Japanese Patent Application Laid-open No. 5-272379 (Patent Document 1).
Also, there is known a configuration in which a gradual-excitation time period is controlled depending on the increase rate of a generator torque to suppress a variation of a battery voltage, an engine output power is corrected depending on the increase rate of the generator torque, and the gradual-excitation time period is shortened after the corrections are completed in order to suppress a variation of an engine speed. For example, refer to Japanese Patent Application Laid-open No. 2005-192308 (Patent Document 2).
Also, there is known a configuration in which a gradual-excitation control is enabled when an electrical load is applied, and the gradual-excitation control is disabled if a battery voltage is excessively lowered to keep the battery voltage within a certain range. For example, refer to Japanese Patent Application Laid-open No. 9-107640 (Patent Document 3).
However, the configuration described in Patent Document 1 has a problem in that a timing of an engine speed increase is delayed when a gradual excitation control is in operation, because, in this configuration, it is judged that there is sufficient margin in a power generation amount of the vehicle alternator when the gradual excitation control is in operation. In addition, although this configuration is able to suppress the variation of the engine speed, it is not able to suppress the variation of the battery voltage.
The configuration described in Patent Document 2 has a problem in that a process load of an engine control unit becomes large, because the engine control unit has to always monitor an engine state, a battery state, an electrical load state, and an alternator state. In addition, since a current sensor is connected to the engine control unit through a long harness routed in an engine room, the engine control unit may malfunction due to ignition noise entering the harness.
The configuration described in Patent Document 3 has a problem in that, since an electrical load state is detected on the basis of the battery voltage in this configuration, a secular variation of an internal resistance of the battery makes it difficult to attain stable control.